1. Field of the Invention
The present invention relates to a semiconductor memory device and the fabrication method thereof, and more particularly to a highly integrated semiconductor memory device and the fabrication method thereof, in which the structure of the storage electrode of a capacitor is improved to increase the capacitance of a memory cell having a stack-type capacitor structure.
2. Description of the Prior Art
The development of highly integrated DRAM (Dynamic Random Access Memory) devices has achieved a density four times that of just three years ago, and this trend will continue with the present pace in technical development. Currently, 4 Mb DRAMs are mass-produced, and 16 Mb DRAMs are being rapidly developed to be mass-produced. 64 Mb and 256 Mb DRAMs are actively being studied. Improvement in integration is achieved by decreasing the memory cell area corresponding to a memory unit. Decreasing the size of a memory cell area essentially results in a decrease in storage cell capacitance. Accordingly, a cell's read-out capability is decreased as the soft error rate is increased. Thus, methodologies aimed at increasing cell integration can unwantedly reduce device performance and cause severe problems.
To overcome the drawback of decreased storage cell capacitance due to a decrease in memory cell area, a three dimensional capacitor has been suggested. For example, a stack capacitor, a trench capacitor, or a stack-trench combined capacitor are commonly used. However, as demand for higher packing density further increases, i.e., from 64 Mb to 256 Mb, achieving highly integrated semiconductor memory devices using simple three dimensional capacitors becomes onerous.
Accordingly, several integrated circuit fabrication techniques have been proposed to overcome the difficulty of preserving high capacitance in manufacturing 64 Mb and 256 Mb DRAMs of three-dimensional storage electrodes. They include: a storage electrode of fin structure in IEDM, 1989, by T. Ema et al. at the Fujitsu Institute; a storage electrode of box structure in SSDM conference, 1989; a storage electrode of a spread stacked capacitor (SSC) structure in IEDM, 1989, by S. Inoue et al. at the ULSI Institute of Toshiba; and a storage electrode of cylindrical structure in a VLSI technology symposium, 1989, by W. Wakamiya et al. at the LSI Institute of Mitsubishi.